i have two male fire red gouramis in my 37 gallon tank. along w/ 4 cory's, 6 platy and 6 danios. today one of my gouramis is barely swimming, it is mostly moving with the water. it seems to have problems staying upright as well, keeps laying on its side. now it is swimming crazy, upside down and into the sides of aquarium. it will fall to the bottom and lie upside down. i see no sign of physical trauma, although it seems pale. nitrates were getting high yesterday and did a 25% water change today. the other fish seem to be fine. any idea about this fish? i do believe i am going to lose it